It is known to oligomerize low boiling range olefins into higher value products that have higher boiling points. For example, some oligomerization processes, process a feed stream comprising C4/C5 olefins and convert these components into diesel range products, as well as some gasoline blending components. In some refineries, the stream comprising C4/C5 olefins may originate from a fluidized catalytic cracking (FCC) unit.
The oligomerization of the C4/C5 olefins from an FCC utilize a catalyst that is sensitive to many contaminants contained in the feed stream. Accordingly, the feed stream to an oligomerization zone is typically treated in a pretreatment section to remove the various contaminants and inhibitors.
Typically, a pretreatment section contains various removal zones each configured to remove contaminants, such as sulfur compounds, di-olefins, oxygenates, nitriles or other contaminants or inhibitors that may be in the feed stream. Thus, a nitrile removal zone typically includes a nitrile removal unit (NRU) which is used to remove the trace levels of nitriles contained in the feed stream. The NRU is typically a swing bed adsorption system that requires an external regenerant stream to refresh the adsorbent bed by desorbing or removing the nitriles from the adsorbent.
In a conventional NRU, the regenerant stream is typically a C4 or C5 hydrocarbon stream that is free of these contaminants. This regenerant stream is vaporized and the spent adsorbent bed is heated with the vaporized stream and the contaminants are removed from the adsorbent. The unwanted contaminants, removed from the feed stream, are now transferred to the spent regenerant stream and the refreshed adsorbent bed is ready to be placed back on-line.
While these processes are presumably effective for their intended purposes, such regeneration processes rely upon a regenerant stream that may not be readily available in some or most refineries. Additionally, while an externally produced regenerant stream could be used, such streams can be costly.
Accordingly, it would be desirable to have one or more processes that efficiently and efficiently allow for the regeneration of a nitrile removal zone that do not require a C4/C5 vaporized regenerant stream. It would also be desirable if one or more of such processes utilized a regenerant stream that is readily available in most refineries.